In one such known yarn monitoring device, a sensing part of the sensing arm extending horizontally in the longitudinal machine direction lies against the yarn section extending between the yarn guide eye and the feed roller, wherein further guide rollers can optionally be provided above the guide part and below the feed roller. If a yarn breakage occurs, the sensing part loses its support by the yarn and the sensing arm swings down until one end of the slot of the mounting bush comes into abutment against the stop pin. The sensing arm then assumes a substantially horizontal position, whereby a yarn clip comes into the region of rotation of the yarn section running from the supply spool to the upper end of the yarn guide tube of the doubling spindle. The rotating yarn section is caught by the clamp device and further yarn takeoff from the supply spool thereby interrupted. Moreover, a red signal plate is fixed on the free end of the sensing arm, which stands out beyond the longitudinal side of the machine, when the sensing arm has fallen into its horizontal position as a result of a yarn breakage.
The projecting red marker signals the yarn breakage to the operator. On dealing with the yarn breakage and on renewed operation of the spindle the sensing arm would be in the path. However it would interfere with the twisting while the spool yarn tension was not attained between the yarn guide eye and the feed roller. For this reason, each sensing arm can be individually swung up with respect to the rocker shaft and it can be held in this swung up position by a support arm of the yarn guide eye, in that this support arm is swung to the side out of its normal position. This holding for the sensing arm is satisfactory for threading the yarn into the twisting spindle and also for changing the supply spool. On twisting however, the thread guide eye must be swung back again into its normal position and then the sensing arm loses its support. So that the sensing arm shall not interfere with the further guiding of the thread and the twisting, while the full yarn tension has not been attained, it must initially be held manually. This is however disadvantageous since one has only one hand available for guiding the yarn. Furthermore, it has been found that severe wear occurs in the mounting bush of the sensing arm in the region of the slot. In fact the mounting bush consists of diecast aluminum because of its varying form, the stop pin however of steel. As a result of the unavoidable vibrations of the machine the stop pin works itself gradually into the material of the mounting bush.
This invention is based on the problem of providing a yarn monitoring device for a doubling machine of the kind initially mentioned, which is operator-friendly when threading and with which moreover the mentioned wear is avoided.
This is attained in accordance with the invention, in that a lining is arranged in the slot in the form of a substantially U-shaped clip of spring steel, whose semi-circular connecting part joining the two U-arms lies at the end surface of the slot directed away from the spindle and whose U-arms extend parallel to the sidewalls of the slot, lie against these and are bent inwardly at their free ends so that the mutual spacing of the two U-arms is somewhat smaller at their free ends than the diameter of the stop pin, and in that the two free ends grip on to the step pin in the swung up position of the sensing arm.
The clip of spring steel arranged in the slot has two functions. In the swung up position of the sensing arm it serves to arrest the same. Consequently the sensing arm can be arrested in the swung up position independently of the support arm of the yarn guide eye. The yarn guide eye can consequently be swung into its central position above the spindle axis at the appropriate time when threading and the operator still has both hands free for further guiding of the yarn over the guide rollers and the feed roller to the winding up spool. This is particularly important with fine yarns. Only when the yarn is completely in position and also the full yarn tension is attained in the yarn section between yarn guide eye and feed roll, is the sensing arm pressed down against the holding force of the clip, until its sensing part lies against the yarn section between yarn guide eye and feed roller. Furthermore the clip serves as a lining for the bounding walls of the slot. Since the clip consists of spring steel, wear of the clip is not to be feared and wear of the mounting bush itself is avoided. Since the clip consists of spring steel it can be made relatively thin. This has the further advantage that the clip can even be retrofitted to existing yarn monitoring devices of the kind in question, in which wear has already appeared in the mounting bushes or further wear is to be avoided.